1. Field of the Invention
The present invention relates to a typefont wheel and a typefont belt for use in a small printer in which the typefont belt made, for example, of rubber and fitted around a cylindrical support to compose a typefont wheel, is struck by a printing hammer provided inside said support to perform printing on a printing sheet.
2. Description of the Prior Art
In a conventional small printer employing a typefont wheel wherein a typefont belt for example, of rubber and fitted around a cylindrical support member is struck by a printing hammer provided in said support member, to perform printing, the typefont wheel and the typefont belt have various drawbacks.
Some of the drawbacks are related to the service life. For example, the typefont belt fitted on the support member is often disengaged from the support member. Also, the ink may extrude from the partially disengaged portion.
The conventional typefont wheel for small printer is composed of a typefont belt 1 as shown in FIG. 1 fitted around a cylindrical or roller-shaped support member 2 as shown in FIG. 2 (hereinafter referred to cylindrical support member). As shown in FIG. 1, the belt 1 is provided on the surface thereof with type portions 1a and type base portions 1b positioned thereunder, and further with corresponding pin portions 1c extending downwards to be fitted in plural holes 2a provided on the support member 2 shown in FIG. 2. Also under the blank type portions 1f there are provided connecting pins 1e which are bonded with an adhesive material to connecting recesses 1g. Similarly a belt portion 1d is bonded with an adhesive material to a belt portion 1h. Said blank type portions 1f are provided as timing spaces for the paper advancing function. Inside said typefont wheel there is provided a printing hammer H as shown in FIG. 4,A printing sheet and a platen are positioned in facing relationship to the type portions 1a on which printing ink is applied by an ink roller 5 shown in FIG. 3.
In the above-explained structure, the typefont wheel is rotated by a motor (not shown) to a position where a pin 1c is positioned in front of the hammer H, and the hammer H is driven towards the left to strike said pin 1c, thereby bringing the type portion 1a into contact with the printing sheet to perform printing thereon. In such a system, in fitting the typefont belt 1 around the cylindrical support member 2 and bonding the edge of said belt, the connecting recesses 1g at an end of the typefont belt 1 are at first inserted into the holes 2a of the support member 2 as shown in FIG. 3, and the connecting pins 13 at the other end of the belt 1 are fitted thereon with an adhesive material 4 therebetween.
The adhesion is, preferably, completed within several seconds to several minutes, but a longer adhesion time is required for example in case of bonding the typefont belt 1 made of silicone rubber with a silicone adhesive material. For this reason, one has to hold the bonded portion for a time and use complicated jigs in order to obtain complete adhesion. In case of incomplete adhesion, the belt portion 1d becomes separated from the belt portion 1h to form a gap as shown in FIG. 3 due to the limited adhering area. If the ink roller 5 is maintained in contact while the typefont wheel is at a standstill or is rotated, the ink intrudes into the gap between the belt portions 1d and 1f, and eventually into the space between the typefont belt 1 and the support member 2. introduced ink causes sticking or adhesion between the typefont belt 1 and the support member 2 which is extremely detrimental to the function of the printing hammer positioned inside the typefont wheel, since the printing energy has to be significantly increased in order to avoid unsatisfactory printing such as totally or partially lacking characters.
Also such a conventional structure as explained above, has manufacturing drawbacks. In such a structure, the cylindrical support member 2 is inevitably expensive as it is provided with a plurality of radially oriented holes 2a which have to be formed with drills or presses and by time-consuming operations.
Furthermore, such a conventional structure has drawbacks in the printing quality.
As shown in FIG. 4, the typefont wheel 7 is rotated by an unrepresented control device and is stopped at a position where the pin portion 1c of a selected character or symbol faces the hammer H, which is then driven towards the left to print said character or symbol on the printing sheet 9 positioned on the platen 8. In order to improve the printing efficiency, the typefont belt is usually made of an elastic material having a high degree of softness, such as A30.degree. C. to A50.degree. C., in the hardness range. Such a typefont belt, however, tends to cause a smear on the printing sheet in certain characters or symbols having small type areas such as "-" or "." because of the contact of the shoulder 16b of the type base with the printing sheet when the type is driven into contact with the platen 8 by the hammer H. Such a smear deteriorates the printing quality and significantly reduces the efficiency of the printer itself.
On the other hand, a harder rubber, if employed for the typefont wheel in order to prevent such a smear, may result in partly lacking print due to deficient printing pressure in types with large areas, such as "0" or "8"